SGERG-88 Details
SGERG-88 (Simplified GERG) is a simplified equation of state for computing the compressibility factor (Z-factor) of natural gas from four measurable bulk parameters: superior calorific value (Hₛ), relative density, hydrogen content, and carbon dioxide content. Unlike the full AGA8 method, it requires no detailed gas chromatographic composition analysis, making it practical for routine billing and custody transfer.

In Germany, SGERG-88 is the basis for the billing compressibility factor (Abrechnungszustandszahl K) defined in DVGW Arbeitsblatt G 685.

SGERG-88 Application Restrictions:
Pressure: 0 MPa to 12 MPa (0 to 120 bar)
Temperature: 263 K to 338 K (−10 °C to 65 °C)
Superior Calorific Value: 30 MJ/m³ to 45 MJ/m³ (≈ 8.3 to 12.5 kWh/m³)
Relative Density: 0.55 to 0.80
H₂ content: 0 to 0.10 mol/mol
CO₂ content: 0 to 0.20 mol/mol

SGERG-88 References:
ISO 12213-3:1997 Natural gas — Calculation of compression factor — Part 3 (paid)
DVGW Arbeitsblatt G 685-6 — Abrechnungsbrennwert und Abrechnungszustandszahl